Jeff Tracy is driving Brains up the wall by demanding he design a spectacular new rescue vehicle, a Thunderbird 6, and then constantly rejecting all his efforts. Still, at least Brains got further with an airline company when he designed a revolutionary airship for them. "Skyship One."
Alan, Tin-Tin, Lady Penelope and Parker represent International Rescue on Skyship One's round-the-world maiden flight, unaware that criminal mastermind TheHood is once again plotting to acquire the secrets of the Thunderbird machines. Paid agents of the Hood murder the original crew of Skyship One prior to take-off and assume their identities, entertaining the guests while scheming to lure the Tracy brothers into a trap. Meanwhile, Brains' efforts to produce a satisfactory design concept for Jeff's proposed Thunderbird 6 collide with fate when Skyship One is damaged and Alan's old Tiger Moth biplane appears to be the only hope of saving the International Rescue group and their impostor hosts.